Subject: Applicability of Tuneup Tips for late model ETX-125's
Sent: Saturday, May 3, 2008 12:09:32
From: Lorenzo Rota
thanks for great site.
I have a "late model" ETX-125AT ( 1-2 yrs old vintage ) and was
wondering how applicable are the Dr. Sherrod tuneup tips( titles listed
below) to newer ETX-125's?
Since some of these tips are 5+ years old, I was wondering if maybe the
designs were improved to correct these problems??
Mainly I am interested in tips to tighten up the play in DEC and RA
axis. I am pretty familiar with the training procedures...so just
looking for mechanical tuneup tips.
I wasn't clear if some of these tuneup tips only pertained to the
earlier models that didnt have the cast aluminum forks.
Any clarification is appreciated.
Thanks,
Lorenzo Rota
Performance Enhancement
Creating The Perfect "GO TO" ETX or LX 90 Part 1 - Mechanical Considerations and Adjustments
German translation (10/04/03)
Part 2 - AutoStar Downloads and Post-Download Initialization (10/31/02)
German translation (10/07/03)
Part 3 - Training the Drives and Celestial Alignment
German translation (10/07/03)
Part 4 - Eliminating Common "Rocking" in ETX Altitude Axis (9/11/02)
German translation (10/07/03)
Part 5 - Polar Alignment Position (3/28/01)
German translation (10/07/03)

From: P. Clay Sherrod (drclay@tcworks.net)
Indeed it would seem to be a "good thing" to update the tune-up tips for
the newer metal mounts on the ETX; however, Meade has not only improved
the strength, reduced the vibration and increased the longevity of the
ETX by going to the newer mount, but they have also pretty much made the
ETX mechanically invasion proof.
Unless a user has very high levels of understanding of the way that this
mount and its wiring are put together, attempting to do something so
simple as get to the drive gear and adjust the torque in the DEC axis
will pretty much render you a pile of bearings, sleeves, shims and more
bearings. Once all the goodies come out, they must be put back together
in a very peculiar way (intentionally) in order for the DEC drive to fit
back into the fork arm trunions.
And the rest of the telescope is even worse for the inexperienced.
My rule on the newer metal interior ETX: if you cannot open up
something and immediately SEE what you are getting ready to "fix", then
leave it alone.
Dr. Clay
-------------
Arkansas Sky Observatories
Harvard MPC/ H43 (Conway)
Harvard MPC/ H41 (Petit Jean Mountain)
Harvard MPC/ H45 (Petit Jean Mtn. South)
http://www.arksky.org/

And:

Thanks to you both for the update.
Dr. Sherrod,
I did as you recommended for the RA axis in the base....I only opened
the bottom for inspection and found the typical "blob of grease" on the
RA motor encoder wheel...which I cleaned off.
I have not yet inspected the DEC axis. Is it still safe to remove the
OTA from the fork and remove the fork covers to inspect the encoder
wheel on DEC axis for same problem?
Main reason I wanted to check was I had been noticing occasionally a
tiny periodic "skipping" when viewing planets and I figured there might
be some dirt/grease in one of the encoder wheel slots.
Again, many thanks to you both for the great contributions to all ETX
users.
Regards
Lorenzo Rota

And:

Although you can remove the OTA by removing the four hex head bolts, two
at each OTA adapter arm, it is not as easy a with earlier models....the
OTA does not snap out easily and much care must be taken to keep from
breaking the locking pins that secure the front of the OTA to the front
portion of the OTA adapters. Nonetheless, you can get it off.
Once off, you can remove the covers....all that you need to remove will
be the OUTER cover, so this means that you do NOT need to remove the
right OTA adapter from the drive unit; this is what can lead to many
pieces that unless put back in the proper order, can cause major
headaches for you. Once the OTA is removed, unscrew all inner Philips
screws from the inside of the right fork arm; this will allow you to
separate the outer half from the inner plastic half. Most of what you
need to inspect will be exposed from the outside, so no need to remove
the inside plate (plastic cover).
If you DO need to get to the mechanism in there, you can carefully push
the OTA adapter and the trunion bearing shaft out of the fork arm; to do
this, you MUST be ready to "catch" all pieces from the inside of the
fork arms as they pass out of the metal bearings. I use a screwdriver
blade inserted into the opening and they all slide off in the proper
order for reassembly once done. When you get that assembly out, keep it
all intact and in order.
Note that you likely will not be able to simply push all of the
components out easily; typically I have to tap on the outside axle using
a wooden dowel and very small ping hammer to force the assembly out of
the hole (trunion opening). Several very carefully lined up taps will
be necessary and do NOT do this without the wooden dowel or you will
damage the assembly.
Remove the inner plastic half and service what you need to. When
re-inserting the OTA and drive assembly back into the fork trunion and
bearings, there is a "key" alignment pin in several of the metal
components....all of these must align to that pin for the assembly to
fit back in.
Like I say....a bit of "no man's land" inside these new ones, but it can
be done. Proceed slowly and with great deliberation. No need to get in
a hurry.
Best of luck.
Dr. Clay